How to display the sum of a column in sqlitedatabase in a textView android?

help me out to get the sum of a column in sqlitedatabase android to a string so that I can view it on a textview I'm a newbie at this. I have a logic to find the sum

this is my ACTIVITY.java

public class CollectionDetailsActivity extends AppCompatActivity { 
TextView daily, monthly; 
SqliteDatabase mydb; 
@Override
 protected void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_collection_details); 
daily= findViewById(R.id.dayCollection);
 monthly = findViewById(R.id.monthCollection); 
SimpleDateFormat date = new SimpleDateFormat("dd/MM/yyyy"); String timeStamp = date.format(new Date()) ; Toast.makeText(getApplicationContext(), timeStamp, Toast.LENGTH_SHORT).show(); 
String data = " "; 

Cursor dailyCollection = mydb.dailyCollection(timeStamp); 
if (dailyCollection.moveToNext()) {
 data = String.valueOf(dailyCollection.getColumnIndex("total")); 
Toast.makeText(getApplicationContext(), data, Toast.LENGTH_SHORT).show(); }
else{ Toast.makeText(getApplicationContext(),"nothing here!! " , Toast.LENGTH_SHORT).show(); } 
daily.setText(data); 
} 

But I can't get it to display on the textview. Somebody please help me.!

this is my Database function

public Cursor dailyCollection(String timeStamp) { 
SQLiteDatabase db = this.getReadableDatabase(); 
String sql2 = "SELECT SUM ("+COLUMN_CM_C_AMOUNT+")AS total FROM "+TABLE_MONEY_COLLECTION+" WHERE "+COLUMN_CM_DATE + "=?"; 
String balance= "0"; 
Cursor cursor = null; 
if (db != null) { 
cursor = db.rawQuery(sql2, new String[]{timeStamp}); 
}else { Toast.makeText(context,"Not Availbel Yet",Toast.LENGTH_SHORT).show();
 }
 return cursor; 
}

this what i am getting

E/com.ancorp.apl: Invalid ID 0x00000000. 
D/AndroidRuntime: Shutting down VM 
E/AndroidRuntime: FATAL EXCEPTION: main Process: com.ancorp.aplo, PID: 5641 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.ancorp.aplo/com.ancorp.aplo.activity.CollectionDetailsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.database.Cursor com.ancorp.aplo.database.SqliteDatabase.dailyCollection(java.lang.String)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3488) at android.app.ActivityThread